The present invention relates in particular to a measuring object for use in a heating apparatus for the thermal treatment of substrates and to a method for manufacturing the same. In use the measuring object has a temperate relation to the substrate to be treated which is in substance known and a surface having at least one surface area, which is used as a measuring area for an optical temperature measurement. Furthermore, the present invention relates to an apparatus for the thermal treatment of substrates, which uses a measuring object of the previously mentioned type.
In the art, different apparatuses and methods for the thermal treatment of substrates are known, as well as apparatuses for determining the temperature of a substrate during a thermal treatment thereof.
A known method for the thermal treatment of substrates, for example provides heating by means of electromagnetic radiation, which is emitted by lamps, for example tungsten halogen lamps. For a closed loop temperature control of the thermal treatment it is known to determine the temperature of the substrates by means of a radiation meter, which is directed onto the substrate or a measuring object, which has a temperature relation to the substrate to be treated which is in substance known. Since, the radiation meter, however, does not only detect radiation emitted by the semiconductor wafer, but in particular also radiation which is reflected by the semiconductor wafer and in some instances also radiation which is transmitted through the semiconductor wafer, it is necessary to distinguish the radiation proportions for the determination of the temperature.
For such a differentiation, U.S. Pat. No. 5,318,386 describes the so called Ripple-technique, in which a modulation is impressed onto the radiation or heat source by means of respective actuation thereof. The modulation originally used was the mains frequency of the power supply and over time the technique was fine tuned and other modulations were used. Temperature changes of the semiconductor waters occur much slower than the impressed modulation. Thus, the radiation which is emitted by the semiconductor wafer due to its own temperature has negligible (if at all) portions of the impressed, sufficiently fast radiation modulation. The detected modulation proportion in the radiation meter may thus be assigned only to the reflection at the substrate and by measuring or modelling the (modulated) radiation proportion of the heating source and by using appropriate algorithms may be used for calculating the reflectivity and emissivity, respectively of the substrate.
For a temperature measurement, using this technique, it is further necessary to determine the emissivity of the measuring object and subsequently the temperature thereof. The emissivity of an object may depend from the temperature or process reactions and may change in a continuous or discontinuous manner throughout the thermal treatment, wherein the change may be reversible or not. In particular, fast changes of the emissivity may lead to disruptions in the temperature measurement, if the emissivity is determined too slow or not determined at all. The calibration of an emissivity measurement is often difficult, since stable references are not present.
Furthermore, the emissivity of an object also depends on its environment and may thus be significantly different in an in-situ/ex-situ measurement.